This invention relates to a composition containing an addictive substance and a component which inhibits the development of tolerance to and/or dependence on the addictive substance. More particularly, the invention relates to a composition containing an addictive substance such as morphine or codeine and at least one nontoxic substance that blocks the N-methyl-D-aspartate (NMDA) receptor, e.g., a morphinan such as dextromethorphan or dextrorphan, or that blocks at least one major intracellular consequence of NMDA receptor activation, e.g., a ganglioside such as ganglioside GM.sub.1 or GT.sub.1b, a phenothiazine such as trifluoperazine or a naphthalenesulfonamide such as N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide.
Morphine is a rapid and effective drug for the treatment of severe pain but its long term administration has been limited due to its negative side effects, principally tolerance and dependence, which develop rapidly after administration. In an effort to make morphine of greater use in the treatment of pain, it has been combined with a variety of substances intended to inhibit one or more of its undesirable side effects. U.S. Pat. No. 2,770,569 describes the combination of morphine with the compound levo-d-hydroxy-N-allyl-morphinan which is said to suppress or eliminate such undesirable side reactions of morphine as depression, nausea and vomiting. U.S. Pat. No. 4,126,684 discloses reducing either the addiction liability of an addictive substance such as a narcotic analgesic or a barbiturate or the withdrawal symptoms caused by deprivation of such a substance in an addicted subject by administering the addictive substance, e.g., morphine, with a 4-amino-3-p-halophenylbutyric acid. U.S. Pat. No. 4,415,871 describes the prevention of treatment tolerance and physical dependence in chronic morphine treatment by combining the morphine with any of the specific dipeptides indicated therein. U.S. Pat. No. 5,041,446 discloses inhibiting the development of tolerance to morphine by combining the morphine with dapiprazole. U.S. Pat. No. 5,057,519 achieves a reduction in morphine tolerance by combining the morphine with a benzamide antagonist for a subtype of the serotonin receptor, 5-HT.sub.3. Trujillo et al., "Inhibition of morphine tolerance and dependence by the NMDA receptor antagonist MK-801", Science, 251 (4989), pp. 85-87, Jan. 4, 1991; Tanganelli et al., "Glutamate antagonists prevent morphine withdrawal in mice and guinea pigs", Neuroscience Letters, 122(2), pp. 270-272, Jan. 28, 1991; Marek et al., "Excitatory amino acid antagonists (kynurenic acid and MK-801) attenuate the development of morphine tolerance in the rat", Brain Research, 547(1), pp. 77-81, Apr. 26, 1991; and, Marek et al., "Delayed application of MK-801 attenuates development of morphine tolerance in rats, Brain Research, 558(1), pp. 163-165, Aug. 30, 1991 discuss the role of MK-801 (the compound 5-methyl-10,11-dihydro-SH-dibenzo[a,d]cyclohepten-5,10-imine), an NMDA receptor antagonist or blocker, in reducing morphine dependence in laboratory animals. However, MK-801 has been found to be toxic and is therefore unsuitable for pharmaceutical use.